plan: tick Phase 4 commit task — coroutine primitive complete

All Phase 4 work landed across 4 commits (21cb9cf5, 9eb12c66, b78e06a7,
0ffe208e). Phase 5 (string buffer) is next.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

plans/agent-briefings/primitives-loop.md

@@ -142,7 +142,9 @@ using call/cc+perform/resume.
       27 tests: added 10 new — state field inspection (ready/suspended/dead), yield from
       nested helper, initial resume arg ignored, mutable closure state, complex yield values,
       round-robin scheduling, factory-shared-no-state, non-coroutine error. 27/27 OCaml+JS.
-- [ ] Commit: `spec: coroutine primitive (make-coroutine/resume/yield)`
+- [x] Commit: `spec: coroutine primitive (make-coroutine/resume/yield)`
+      Phase 4 landed across 4 commits: 21cb9cf5 (spec library), 9eb12c66 (ocaml verified),
+      b78e06a7 (js pre-load), 0ffe208e (27 tests). Phase 4 complete.
 
 ---
 
@@ -674,6 +676,7 @@ Brief each language's loop agent (or do inline) after rebasing their branch onto
 
 _Newest first._
 
+- 2026-04-26: Phase 4 complete — coroutine primitive fully landed (4 commits: spec library + OCaml verified + JS pre-load + 27 tests). Phase 5 (string buffer) next.
 - 2026-04-26: Phase 4 Tests step done — 27 tests total (10 new: state field inspection, yield-from-helper, initial-arg-ignored, mutable-closure, complex-values, round-robin, factory-no-state, non-coroutine-error). 27/27 OCaml+JS.
 - 2026-04-26: Phase 4 JS step done — all CEK primitives already in sx-browser.js; fix was pre-loading spec/coroutines.sx+spec/signals.sx in run_tests.js so (import (sx coroutines)) resolves synchronously. 17/17 coroutine tests pass JS. 1965/2500 total (+25), zero new failures.
 - 2026-04-26: Phase 4 OCaml step done — no native SxCoroutine type needed; existing cek-step-loop/cek-resume/perform/make-cek-state primitives in run_tests.ml fully support the spec/coroutines.sx library. 284/284 pass (coroutines+vectors+numeric-tower+dynamic-wind), zero regressions.